Issue Rendering Hollow Objects
there's nothing wrong, and actually you can look inside of those objects. your lamp (probably a sunlamp) is directly above your scene and lights everything inside of the objects in the same way. so there are no shadows or reflections that would indicate holes in the cups. try repositioning your lamp if the look bothers you.

Edit:
Don't feel like a fool. perpendicular light always looks a bit odd.
Take this image for example. It's taken on the equator at noon. Looks like a computer game from the early 2000s.